The Physiology Core will support all four projects of this PPG. This core will provide nursing support for the three human research studies. This will enhance the safety of the volunteers over and above the excellent level of care now provided in the General Clinical Research Center (GCRC). This core will also analyze adenine nucleotides and nitric oxide in the muscle interstitium and catecholamines in plasma and in the muscle interstitium. This core will also support the salary of individuals involved in the microdialysis procedures. Having this activity performed within this core will improve quality control and volunteer safety. In addition, this core laboratory will provide the expertise for the non-invasive blood flow measurements to be performed (three projects) and microneurography (three of four projects). Supplies for the various activities will be purchased in bulk. This will contribute to the cost effective function of this core laboratory. This core represents a state-of-the-art facility that will lead to important advances in our understanding of neural control of the circulation. The Physiologic Core Laboratory will provide support for all four of the projects. This core laboratory will provide the following services to the investigators: microneurography, microdialysis, HPLC measurements of plasma and interstitial substances, ultrasound/Doppler measurements of cardiovascular function and the performance of invasive flow studies (see Figure 1). This core will support investigators as they obtain and analyze specimens. The core laboratory will also aid in the performance of the studies and clinical oversight for the human volunteers. Dr. Urs Leuenberger has experience with each of the methods and techniques described in this proposal and is an ideal investigator to ensure quality control of this state-of-the-art laboratory.